LAYTON -- The U.S. Air Force is underestimating the noise and impact that more combat operations would have at the Utah Test and Training Range, military watchdogs and conservation groups say.

The Air Force wants to fly fighter jets more often and at lower altitude over the White Elk Military Operating Area and push the low-altitude operations father into Nevada, officials at Hill Air Force Base in Layton said Saturday.

It also wants to fly jets at supersonic speeds at higher altitudes over the parts of Nevada's White Pine and Elko counties, said Barbara Fisher, an environmental affairs spokeswoman for Hill Air Force Base.

The sonic booms could be heard every other flying day, according to a draft environmental impact statement.

Thursday was the final day for public comment on that document -- and critics had plenty to say, according to accounts in three Utah newspapers.

The Air Force study says the new operations would cover an area of 1.6 million acres, which equals 2,500 square miles.

Sorties over the entire test range would increase to 9,600 a year, up from 400.

Pilots could drop chaff -- explosives filled with aluminum strips to throw off radar-guided missiles -- and flares, which can divert heat-seeking missiles.

"They wouldn't propose doing this over Ogden or Salt Lake City," said Grace Potorti, a member of the Reno, Nev.-based Rural Alliance for Military Accountability.

The 400,000-member Aircraft Owners and Pilots Association says the Air Force failed to look at the effect more military flights would have on civil and commercial aviation. The Air Force study says it took those concerns into consideration.

"This is a new special use air space we're creating underneath our existing air traffic control-assigned airspace adjacent to the Utah Test and Training Range," Fisher said.

Regular sorties could fly as low as 14,000 feet instead of 18,000 feet, she said. Supersonic flights would be conducted no lower than 18,000 feet, she said.

The Air Force expects to make the operational changes by the middle of next year, she said.

On the Net:

• www.accplanning.org